JP2001110965A - Adhesive sheet with high thermal conductivity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an adhesive sheet with sufficient adhesion and thermal conductivity. SOLUTION: An adhesive layer 3 in dot shapes 3a, 3a... or in a mesh shape is provided on both the surfaces of a base sheet 2 that is made of a composition where a heat-conductive filler such as a large amount of BM is filled into silicone rubber cured at ambient temperature with a low modulus and fluidity at ambient temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly heat-conductive pressure-sensitive adhesive sheet used for joining a heat-generating electronic device, for example, a power transistor to a heat sink, and efficiently transmitting heat from the electronic device to the heat sink.

[0002]

2. Description of the Related Art Conventionally, as this kind of highly heat-conductive pressure-sensitive adhesive sheet (hereinafter abbreviated as pressure-sensitive adhesive sheet), those shown in FIGS. 3 and 4 are known. The pressure-sensitive adhesive sheet 1 shown in FIG. 3 is provided with pressure-sensitive adhesive layers 3 and 3 on both surfaces of a base sheet 2. The base sheet 2 has a thermal conductivity of 6 to 10 W in which a large amount of a high thermal conductive filler such as boron nitride, aluminum nitride, or silicon carbide is filled in a silicone rubber having good heat resistance and thermal conductivity.
/ M · k made of a high thermal conductive composition.

[0003] The adhesive layer 3 includes a main material such as ordinary synthetic rubber, natural rubber and acrylic resin, a tackifier such as ester gum, hydrogenated rosin and coumarone resin, phthalate ester, castor oil, and the like. A compound containing a plasticizer such as chlorinated paraffin is used, and its thickness is 20 to 100 μm.
It was a degree.

The pressure-sensitive adhesive sheet 1 shown in FIG. 4 has a reinforcing mesh 4 made of glass fiber or the like interposed between a base sheet 2 and pressure-sensitive adhesive layers 3.
This is a reinforcement.

The pressure-sensitive adhesive sheet 1 having such a structure has a function of bonding a heat generating element such as a heat-generating device to a heat sink, and transferring heat from the heat generating element to the heat sink. Works with conductive material. However, the thermal conductivity of the base sheet 2 is as high as 6 to 10 W / mk due to the high filling of the high thermal conductive filler.
Since the heat conductivity of the adhesive layer 3 is as low as 0.2 to 1 W / m · k, the adhesive layer 3 acts as a heat barrier (heat barrier), and there is a disadvantage that the heat conductivity of the entire adhesive sheet 1 is reduced. .

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent the heat conductivity of the entire pressure-sensitive adhesive sheet from being reduced even if a pressure-sensitive adhesive layer is present.

[0007]

This problem can be solved by forming the adhesive layer in a dot shape or a mesh shape, and by forming a region where the base sheet directly contacts the heating element or the heat sink. In addition, the base sheet shows fluidity at room temperature,
By using a silicone rubber having a low modulus, the direct contact area can be increased.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 shows an example of the pressure-sensitive adhesive sheet of the present invention. The pressure-sensitive adhesive sheet 1 of this example is obtained by forming a dot-shaped pressure-sensitive layer 3 on a base sheet 2. The base sheet 2 is composed of a highly thermally conductive composition obtained by highly filling a highly thermally conductive filler such as boron nitride, aluminum nitride, silicone carbide, etc. in a silicone rubber by about 30 to 80 wt%, and has a thickness of about 0.5 to 4 mm. Sheet.

As the silicone rubber, a room temperature-curable silicone rubber having low modulus and room temperature fluidity is particularly preferable. By using this type of silicone rubber, the base sheet 2 can be used as a heating element and a heat sink. The area of direct contact increases and the thermal conductivity improves.

On both surfaces of the substrate sheet 2, dot-shaped adhesive layers 3 and 3 are formed. Here, the dot-shaped adhesive layer 3 refers to a number of dot-shaped adhesives 3a, 3 made of an adhesive.
a, 3a... As the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer 3, a commonly used pressure-sensitive adhesive is used.
A material filled with the above-mentioned high thermal conductive filler or a material having high adhesive strength may be used.

The shape of the adhesive 3a is arbitrary, such as a circle, an ellipse, or a polygon such as a triangle, and the size is 0.5.
The size is about 0.5 mm to 3 mm x 3 mm. The distance between the adhesives 3a, 3a,.
m, and the thickness is about 10 to 300 μm.
Also, 30 to 50% of the surface area of the base sheet 2 is
If it exceeds 50%, the effect of improving thermal conductivity cannot be obtained, and if it is less than 30%, the adhesive strength is reduced, and the original function as an adhesive sheet is lost.

Further, the adhesive 3a provided on one surface of the base sheet 2 and the adhesive 3 provided on the other surface
a, 3a... are preferably provided so as to be shifted from each other so that they do not exist at the same position on the sheet 2 because the average thickness of the adhesive sheet 1 becomes uniform. 1 is preferable because local variation in the thickness of the base sheet 2 at the time of joining by the method 1 is reduced.

The formation of the dot-shaped adhesive layer 3 is as follows.
For example, a metal sheet in which holes corresponding to a large number of pressure-sensitive adhesives are perforated is placed on the base material sheet 2 and the pressure-sensitive adhesive can be easily applied from above.

In the pressure-sensitive adhesive sheet 1 having such a configuration, the heating element and the heat sink can be joined with sufficient strength by the dot-shaped pressure-sensitive adhesive layer 3. In addition, at the time of joining, by pressurizing both, the low-modulus, room-temperature fluid silicone rubber forming the base sheet 2 is plastically deformed,
In a region where each of the adhesives 3a, 3a,... Does not exist, the high thermal conductive base sheet 2 comes into direct contact with the surface of the heating element or the heat sink, and heat is directly conducted from here, so that the entire adhesive sheet 1 Has improved thermal conductivity.

In the pressure-sensitive adhesive sheet 1 of the present invention, as shown in FIG. 2, the pressure-sensitive adhesive layer 3 may be formed in a mesh shape. In the mesh-shaped adhesive layer 3, the widths of the warp portions 3b, 3b... And the weft portions 3c, 3c.
It is preferably about m to 4 × 4 mm, and the ratio of the area occupied by the adhesive layer 3 is preferably 30 to 50% as in the previous example.

Further, the plane shape of the mesh opening is not limited to a quadrangle but may be an arbitrary one such as a triangle. Even in the pressure-sensitive adhesive sheet 1 of this example, the dot-shaped pressure-sensitive adhesive layer 3
The same operation and effect as those provided with are obtained. Furthermore, when providing a reinforcing mesh made of glass fiber or the like,
It is preferable to embed inside the base sheet 2.

Hereinafter, specific examples will be described. (Experimental example 1) 50% by weight of silicone rubber having low modulus and fluidity at room temperature, boron nitride (average particle size 4
0 μm) An acrylic rubber-based pressure-sensitive adhesive was applied to both sides of a base sheet having a composition of 50% by weight and a thickness of 2 mm to form a pressure-sensitive adhesive layer, thereby producing a pressure-sensitive adhesive sheet. As the adhesive layer, one coated on the entire surface of the substrate sheet and one coated with a circular adhesive having a diameter of 1 mm while changing the interval between the adhesives were prepared. Further, a sheet in which a reinforcing mesh made of glass fiber was embedded in the base sheet was also prepared.

Using these various types of pressure-sensitive adhesive sheets, a heating element and a heat sink were joined, pressed and integrated, and the heat conductivity of the pressure-sensitive adhesive sheets was evaluated using the pressure-sensitive adhesive sheets. The heating element has a surface temperature of 13 without a heat sink.
Those which became constant at 0 ° C. were used. The heating element was heated and the surface temperature of the heating element was measured two hours later. The lower the surface temperature, the better the thermal conductivity of the pressure-sensitive adhesive sheet. Further, the adhesive strength between the heating element and the heat sink was measured. The measurement of the adhesive force was performed by a method of obtaining a stress at the time of peeling between the heating element and the heat sink. Table 1 shows the results.

[0019]

[Table 1]

(Experimental Example 2) In the experimental example 1, the adhesive layer was formed in a mesh shape. The width of both the warp portion and the weft portion of the mesh was set to 1 mm, and the interval was changed.
This adhesive sheet was evaluated for thermal conductivity and adhesive strength in the same manner as in Experimental Example 1. Table 2 shows the results.

[0021]

[Table 2]

In Tables 1 and 2, the surface temperatures and adhesive strengths of Test Nos. 3 to 6 and 10 to 13 are shown as fluctuation values based on Test No. 1. Further, the surface temperatures and the adhesive strengths of Test Nos. 7 to 9 and 14 to 16 are represented as fluctuation values based on Test No. 2.

[0023]

As described above, the highly heat-conductive pressure-sensitive adhesive sheet of the present invention has sufficient adhesiveness and exhibits high heat conductivity. It can be suitably used for bonding or the like.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a highly heat-conductive pressure-sensitive adhesive sheet of the present invention.

FIG. 2 is a perspective view showing another example of the high heat conductive adhesive sheet of the present invention.

FIG. 3 is a cross-sectional view showing an example of a conventional high heat conductive adhesive sheet.

FIG. 4 is a perspective view showing another example of a conventional high heat conductive adhesive sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... High thermal conductive adhesive sheet 2 ... Base sheet 3 ... Adhesive layer

Continued on front page F term (reference) 4F100 AK01A AK52A AN02A AR00B BA02 DC11B GB41 JA06A JJ01 JJ01A JK06 JK07A JL13B 4J004 AA04 AA05 AA10 AB01 CA06 CA07 CC02 CE03 FA05 5F036 AA01 BB21 BD21

Claims (2)

[Claims] An adhesive layer is provided on a surface of a base sheet made of a highly thermally conductive resin composition, and the adhesive layer is formed in a dot shape or a mesh shape. Sheet. 2. The highly heat-conductive pressure-sensitive adhesive sheet according to claim 1, wherein the high heat-conductive resin composition exhibits fluidity at room temperature and is mainly composed of low-modulus silicone rubber.